Total hip replacement is a procedure that is performed over 600,000 times every year worldwide, and up to 350,000 times per year in the United States alone. These procedures involve removing bone and cartilage from the diseased hip and replacing it with metal and plastic to give the patient a smooth articulating and long-lasting hip. Intra-operatively, the surgeon balances the unique bony anatomy of the patient with the limited implant sizing and shape variations made available by each of the manufacturers. To optimize the performance of the hip, the surgeon needs to balance the soft tissue envelope around the hip as well as the mechanical balance of the hip. Achieving this balance within a defined three-dimensional space drives the use of imaging devices, such as intraoperative C-arm x-rays.
An x-ray device outputs images of the patient's pelvic area, the surgeon begins evaluating the leg length, pelvic distance, and cup inclination visually. The hip replacement procedure includes a series of steps that require assessment before moving to the next step. While the intra-operative x-ray is one of the most valuable tools used to perform this assessment, the patient and the position of the x-ray device may unfortunately change during each step requiring a re-registration prior to utilizing the x-ray device. A variation of even a small amount from an optimal position can change the stability, mechanical balance, and potentially the longevity of the hip replacement. Thus, the accuracy of the x-ray image and the analysis thereof are very important stages of the procedure.